Field of the Invention
The present invention relates to an image forming apparatus having a heating and fixing apparatus that thermally fixes, as a fixed image, a non-fixed toner image formed and born on a recording material.
Description of the Related Art
In a conventional image forming apparatus of this type, a recording material on which a non-fixed toner image is formed is passed through a fixing nip portion of a heating and fixing apparatus to apply heat and pressure to the toner image so that the toner image is heated and fixed to the recording material.
A recording material is fed from a cassette or a tray and conveyed to a fixing apparatus with a toner image formed thereon in an image forming unit. However, when the recording material is not set appropriately, the recording material may be skewed so that printing accuracy may decrease and a print jam may occur. Moreover, when the recording material is conveyed in a state of being shifted from a reference position, an excessive temperature rise occurs in a non-sheet-passing area of a heating and fixing apparatus and a temperature rise suppressing technique unintentionally operates to suppress the excessive temperature rise, which may decrease the productivity.
Conventionally, such an image forming apparatus as disclosed in Japanese Patent Application Publication No. 2011-27885 has been proposed as a method for determining conveying faults such as skew or positional error conveying of the recording material.
Japanese Patent Application Publication No. 2011-27885 discloses a method of detecting positional error conveying of a recording material when a temperature difference between both ends of the recording material reaches a predetermined value or higher to control the operation of an apparatus using a temperature detector for detecting an increase in the temperature of a non-sheet-passing portion occurring when a recording material having a small size passes.
However, as disclosed in Japanese Patent Application Publication No. 2011-27885, it is difficult to accurately determine the skew or the positional error conveying of the recording material from a temperature difference between both ends in the longitudinal direction of a fixing apparatus occurring due to sheet-passing. That is, the temperature difference between both ends in the longitudinal direction of the fixing apparatus occurs due to various factors such as a lateral difference in the temperature increase within an image forming apparatus, a sensitivity fluctuation among temperature detectors, or a variation in detection temperature resulting from durability deterioration of members as well as the positional error conveying or the skew of the recording material.
Thus, in this determination method, it is difficult to make determination on the positional error conveying of recording materials with high accuracy and a small number of passing sheets, and a large number of sheets needs to be passed to make determination on the positional error conveying. Moreover, it is difficult to detect temporary skew which causes only a small temperature difference in a longitudinal direction.